Ruby/C3/Object-Oriented-Concept-in-Ruby/English-timed

Time	Narration
00:01	Welcome to this spoken tutorial on Object Oriented Concept in Ruby.
00:06	In this tutorial, we will learn to:
00:08	* use classes
00:09	* creating objects
00:10	* different ways of defining methods in Ruby.
00:13	Here we are using:
00:14	* Ubuntu version 12.04
00:16	* Ruby 1.9.3
00:19	To follow this tutorial, you must have knowledge of Linux commands, Terminal and Text-editor.
00:24	If not, for relevant tutorials, please visit our website.
00:28	Before we begin, recall that we had created a “ttt” directory earlier.
00:33	Let's go to that directory.
00:35	To ruby hyphen tutorial and classes directory.
00:41	Ruby is an object oriented language.
00:44	Everything in Ruby is an object; from a value to a string or number.
00:49	A class' is a collection of related data and functions.
00:53	It can serve to keep information organized.
00:56	An object is an instantiation of a class.
01:00	A class definition begins with the keyword class.
01:05	It is followed by the name of the class.
01:08	It is delimited with an “end”.
01:11	Let us look at an example of a class.
01:14	class Product
01:16	ruby code
01:17	end
01:20	The name of the class must begin with a capital letter.
01:24	Names that contain more than one word should be camelcased.
01:28	For example,
01:30	UserInformation
01:32	ProductInformation
01:34	The subsequent file names will have underscore separating the words:
01:37	user underscore information
01:40	product underscore information
01:45	Create a new file in gedit as shown in the basic level Ruby tutorials.
01:48	Name it class_definition.rb
01:52	I have a working example of the implementation of classes.
01:57	You can pause the tutorial and type the code as we go through it.
02:02	I have defined a class named Order in this example.
02:05	Now, let us make the class useful by adding some variables.
02:11	Then I have defined an instance variable “myinstance”.
02:15	And I have assigned a value to it.
02:18	I have also defined a class variable “myclassvar” .
02:21	And I have assigned a value to it.
02:24	Now, let us add some code that will make use of this class.
02:30	Type: puts Order dot instance underscore variables
02:36	Before this line, add puts some characters slash n for a new line.
02:43	Let us copy and paste that and add it just below the line we added and save it.
02:51	Now, let us execute this code.
02:53	Switch to the terminal and type:
02:56	ruby space class underscore definition dot rb
03:02	and see the output.
03:05	You will see the instance variable you defined.
03:09	Now, let us type: puts Order dot class underscore variables
03:15	Let us copy and paste the demarcation, just below the line and save it.
03:21	Now, let us switch to the terminal and execute the file like before.
03:26	You will notice the class variable you defined, also show up.
03:32	You should now be able to write your own class.
03:35	Next, let us look at what an object is.
03:40	An object is an instance of a class.
03:43	Which means, an object is created from a class.
03:46	An object will have the properties and methods defined in the class.
03:52	How do you declare an object?
03:54	We declare an object of a class using the "new" keyword.
03:58	Here, we are declaring an object of the Product class.
04:02	Here, an object gets created.
04:05	product = Product.new
04:09	This process is called initialization of an object.
04:12	This object is of type Product.
04:16	Now, let is look at what an “initialize” method is.
04:20	An initialize method is called at the time of object creation.
04:26	On calling "new" on an object, we invoke the initialize method.
04:31	An initialize method may take a list of parameters.
04:37	Like other 'Ruby' methods, it is preceded by the “def” keyword.
04:43	Let us look at an example.
04:46	Create a new file in gedit as shown in the basic level Ruby Tutorials.
04:50	And name it object underscore initialize dot rb.
04:55	I have a working example of the object initialization code.
05:00	You can pause the tutorial and type the code as we go through it.
05:04	Here, I have defined a class called “Order” .
05:08	Then I have defined the initialize method, with no argument.
05:13	I have defined a 'puts' method to display the message: “I have created an object”.
05:20	Next, I have defined Order dot new.
05:24	This will invoke the initialize method.
05:27	Switch to the terminal and type:
05:31	ruby space object underscore initialize dot rb
05:36	and see the output.
05:39	You will see the message: “I have created an object”.
05:43	Now, let us go back to gedit and add an argument to the method.
05:48	Let us modify the puts.
05:51	It should display the value of the argument passed.
05:55	Next, let us type:
05:56	Order dot new(“I have created an object”).
06:04	Here, we have given an argument to the "new" method.
06:08	This argument gets passed on to the initialize method.
06:13	Switch to the terminal and type:
06:16	ruby space object underscore initialize dot rb
06:20	and see the output.
06:22	You will see the message: “I have created an object” printed out.
06:29	Now, you would have understood what object initialization means.
06:33	Recall that in Ruby, methods are the functions that a class performs.
06:39	Each method in a class is defined within the “def” and “end” block.
06:45	A multi-word method-name is separated with an underscore.
06:48	Some of the characters that can be appended to a method name are:
06:54	'?' (question-mark)
06:56	'=' (equal to).
06:58	Each of the characters add some meaning to the method.
07:02	Let us look at some examples.
07:05	Create a new file in gedit as shown in the basic level Ruby tutorials.
07:09	And name it class underscore methods dot rb.
07:14	I have a working example of class methods code.
07:17	You can pause the tutorial and type the code as we go through it.
07:21	Here, I have defined a class named “Animal”.
07:23	Then I have two methods- “breathe” and “walk”.
07:28	They are both defined with the “def” and “end” keywords.
07:32	I have then initialized the object 'Animal'.
07:36	I have assigned it to a variable called “animal” with lowercase “a”.
07:40	Then I have invoked the methods “breathe” and “walk” consecutively.
07:48	Now, let us execute the program.
07:51	Switch to the terminal and type:
07:53	ruby space class underscore methods dot rb
07:58	and see the output.
08:00	You will notice the lines:
08:02	“ I breathe”
08:03	“I walk”
08:04	printed out.
08:05	This is because you have invoked the two methods “breathe” and “walk”.
08:10	A “puts” statement, defined within these methods, gives the results you see.
08:16	Next, let us look at how to create methods with a trailing question mark (?).
08:21	Create a new file in gedit as shown in the basic level Ruby tutorials.
08:25	And name it class underscore methods underscore with underscore trailing underscore characters dot rb.
08:35	I have a working example of class methods with question mark code.
08:40	You can pause the tutorial and type the code as we go through it.
08:45	Here, I have taken the same class as before, as an example.
08:48	Here, the "breathe" method has a trailing question mark (?).
08:52	Such methods are generally used to return Boolean values.
08:55	This is based on the method naming convention of Ruby.
09:00	The method gets invoked by declaring animal dot breathe question-mark.
09:06	Switch to the terminal and type:
09:09	ruby space class underscore methods underscore with underscore trailing underscore characters dot rb and see the output.
09:22	You will notice the output as : “true”
09:26	Next, let us define another method called “walk”.
09:30	Let us place an equal-to sign “=(value)” beside it.
09:36	Let us invoke this method by calling animal dot walk.
09:41	Then let us execute this method.
09:44	Switch to the terminal and type:
09:45	ruby class underscore methods underscore with underscore trailing underscore characters dot rb
09:52	and see the output.
09:56	It will give an “undefined method” error.
09:59	This is because the equal to sign has another meaning.
10:03	It is used to assign a value to a method.
10:08	So, let us invoke the method a little differently this time.
10:13	Type: puts animal dot walk equal to “hops”.
10:17	Now, let us give it another try.
10:20	Switch to the terminal and run the command like before and see the output.
10:27	You will notice that the word “hops” get printed.
10:30	This demonstrates that the equal to sign (=) next to a method means assignment.
10:36	Now you should be able to write your own methods.
10:42	In this tutorial, we have learnt:
10:44	* How to declare classes
10:46	* How to create objects of a class
10:48	* Different ways of defining methods in Ruby.
10:52	As an assignment:
10:54	Define a class Product
10:56	Define methods that you can use to get values of “myvar” and set values for “myvar”.
11:01	To set values, define the method using “=” sign.
11:05	Instantiate the object of the class and set and get values using the above 2 methods.
11:12	Watch the video available at the following link.
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11:56	This is Anjana Nair, signing off. Thank you.

Contributors and Content Editors

Jyotisolanki, PoojaMoolya, Pratik kamble, Sandhya.np14, Shruti arya